This is sort of strange. If you have been doing weekly 25% water changes with gravel vaccums and it's been three months, even if you were fishy cycling, the cycle should be over by now. I would scower the tank and check for anything and everything that could be decaying. The filter you are using is good-if it's an aquaclear 20-though most of us like to overfilter our tanks. I have an aquaclear 20 and a whisper 10 on my 10 gallon, for example. Check the expiration date of your test kit and overdose prime or amquel +, also. What type of liquid test kit are you using?
If you friend has livebearers(mollies, guppies, platies, swordtails are some livebearers)that are commonly sold it would be almost impossible for her to NOT have babies. You can have an ammonia spike and still have crystal clear water.